1. Field of the Invention
The instant invention relates to a method and an apparatus for power IC heat sinking which provides positioning and clamping forces using a package case/cover for direct mounting heat sinking. For the "Spruce" method of heat sinking in accordance with the invention, the electrical components are not heat sunk until the cover of the casing assembly is attached to the circuit board.
2. Description of Related Art
Most electrical components generate thermal energy. Some such devices generate so much heat that the device itself may be damaged or may operate improperly unless excess thermal energy is removed during operation. Mechanical and thermal contact assemblies in the form of heat sinks of various forms are conventionally used to protect electronic devices from excess heat. Typically, mechanical and thermal contact assemblies require additional mounting structures, such as rivets, screws, or other hardware, to attach or contact the electrical component to the heat sink. In an effort to eliminate the additional mounting structures, the prior art teaches the use of spring clips to attach the electronic components to the heat sink(s).
Generally, there are two methods presently used for mounting the heat generating electrical components to a heat sink. The first method mounts the component in a conventional manner to the heat sink (parts stand perpendicular to the circuit board) and the necessary normal forces are provided by a plastic clamp, compressing the component to the heat sink. An example of this method is shown in FIG. 1. However, the method of FIG. 1 requires additional fasteners which increases assembly time. Over time these fasteners may become disengaged thus reducing heat transfer efficiency.
As shown in FIGS. 1 and 2, conventional heat sink arrangements require clamps 2 and fasteners 4 to attach the electrical component 1 to the heats sink 6. As shown in FIG. 3, this arrangement sandwiches the heat generating component 1 between the clamp 2 and the heat sink 6 to ensure proper thermal contact therewith. This arrangement incurs the drawback of increased assembly time and often results in the loss of proper thermal contact when the fastener become disengaged.
A second method mounts the electrical component directly to the controller case referred to as alternate lead form (ALF) mounting, and the necessary clamping forces are generated when the joining case halves are fastened together, an example of this prior art is shown in FIG. 4.
FIG. 4 illustrates a conventional arrangement whereby the heat generating component 1 is positioned on its side on the circuit board 11, and the casing enclosure 13 provides the clamping force to ensure proper thermal contact between the component and the heat sink. However, this second method serves to greatly reduce the usable circuit board area after assembly.
U.S. Pat. No. 5,060,112 issued on Oct. 22, 1991 to A.G. Cocconi also discloses an electrical component assembly with a heat sink and a method for providing the assembly with leaf springs for improving the thermal contact between the heat generating components and the heat sink. However, this arrangement is difficult to assemble and requires a number of functional parts.